Polyolefin plastic has been considered non-biodegradable conventionally, and it has been known that only about 1% of polyethylene as a polyolefin plastic is decomposed after 10-year bacterial treatment (Journal of Applied Polymer Science, 35, 1288-1302 (1988)).
Also, it is known a method for decomposing polyamide plastic by means of a bacterium (Flavobacterium sp. K172) (Agr. Bio Chem., 39 (6), 1219-1223(1975); Hakkoukougakukaishi, 60(5), 363-375(1982)). However, all of these conventional methods concerning polyamide plastic are classified in the method for treating water-soluble, low-molecular nylon 6 oligomer (molecular weight of about 2,000 or less). Thus, water-insoluble, high-molecular nylon (molecular weight of about 10,000 or more) cannot be decomposed with these methods.
It has been known a biodegradable composition which has been modified for ready biological attack by dispersing starch in a thermoplastic synthetic resin (Japanese Patent Laid-open No. Sho 49-55740). In the biodegradable composition, however, it is only the starch particle that is decomposed biologically, whereas the synthetic resin cannot be decomposed. That is, the composition is just degraded when the starch particle is not any more decomposed, so the synthetic resin still remains.
For the disposal of plastic waste, the rapid decomposition of plastic waste of itself is an issue of significance. Therefore, such objective cannot be achieved by the conventional methods, as is apparently shown in what has been described above.
Under such current technical circumstances, the present invention has been performed for the objective to prevent plastic pollution. The present invention has been carried out for the objective to provide a method for efficiently decomposing plastic of itself which has never been substantially decomposed by the conventional methods and to provide a plastic suitable for such decomposition method.